Energetic studies and developments are being made as to organic electroluminescent devices, because highly luminescent emission is obtained from these devices with low-voltage driving. The organic electroluminescent devices are constituted of an organic layer and a pair of electrodes between which the organic layer is sandwiched. In such devices, electrons injected from the cathode are recombined with holes injected from the anode in the organic layer, to produce excitons, whose energy is utilized to emit light.
Improvement in the efficiency of devices has been recently made by using a phosphorescence-emitting material. Iridium complexes, platinum complexes, and the like are such a phosphorescence-emitting material (see, for example, U.S. Pat. No. 6,303,238 and WO 00/57676). However, devices having both high efficiency and high durability have not been developed. Therefore, there has been a need for development of phosphorescent materials capable of satisfying both.